It is often desirable to non-invasively monitor or measure the flow of a fluid, for example in an implanted medical device or in a body, and to be able to communicate or indicate the monitoring or measurement information remotely.
By way of illustration, treatment of hydrocephalus can involve monitoring the flow rate of cerebrospinal fluid through a hydrocephalus shunt. Hydrocephalus is a neurological condition that is caused by the abnormal accumulation of cerebrospinal fluid (CSF) within the ventricles, or cavities, of the brain. CSF is a clear, colorless fluid that is primarily produced by the choroid plexus and surrounds the brain and spinal cord, aiding in their protection. Hydrocephalus can arise when the normal drainage of CSF in the brain is blocked in some way, which creates an imbalance between the amount of CSF produced by the choroid plexus and the rate at which CSF is absorbed into the bloodstream, thereby increasing pressure on the brain.
Hydrocephalus is most often treated by surgically implanting a shunt system in a patient. The shunt system diverts the flow of CSF from the ventricle to another area of the body where the CSF can be absorbed as part of the circulatory system. Shunt systems come in a variety of models and typically share similar functional components. These components include a ventricular catheter, which is introduced through a burr hole in the skull and implanted in the patient's ventricle, a drainage catheter that carries the CSF to its ultimate drainage site, and optionally a flow-control mechanism, e.g., shunt valve, that regulates the one-way flow of CSF from the ventricle to the drainage site to maintain normal pressure within the ventricles. It is this flow of CSF which may need to be measured.
In some cases, measuring the flow of CSF can be accomplished by a flow sensor using temperature differentials between two points, e.g., with a mechanism for heating or cooling the CSF in a particular section of the catheter. However, it would be advantageous to provide a flow sensor capable of more accurate and/or direct measurements of flow, without the need for heating or cooling equipment, and to provide a straightforward way to retrieve the measurements from the sensor. Such considerations can apply to a wide range of applications involving the measurement of gas and fluid flow, including CSF, within an implanted device or an embedded, encapsulated, or relatively inaccessible space.
Accordingly, there remains a need for non-invasive monitoring and/or measuring the flow of a fluid, and more particularly for monitoring and/or measuring the flow of a fluid in an implantable medical device.